Electrodeless plasma lamp systems and methods

ABSTRACT

Systems and methods for an electrodeless plasma lamp as described. A drive probe is coupled to the lamp body to provide the primary power for ignition and steady state operation of the lamp. Feedback is used to adjust frequency in response to changing conditions of the lamp during startup. A phase shifter is used to adjust the phase of the power between ignition and steady state operation. A sensor may detect a lamp operating condition that automatically triggers a shift in phase after the fill in the bulb is vaporized. The phase shift may then continue to be adjusted as the plasma heats up and the impedance continues to change. The bias conditions of an amplifier may be changed to change the operating class of the amplifier for different modes of the lamp.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority to U.S. ProvisionalApplication No. 60/852,289, entitled “SYSTEMS AND METHODS FOR COUPLINGPOWER TO AN ELECTRODELESS PLASMA LAMP,” filed Oct. 16, 2006; U.S.Provisional Application No. 60/852,326, entitled “PLASMA LAMP SYSTEMSAND METHODS USING MULTI-MODE AMPLIFIER,” filed Oct. 16, 2006; and U.S.Provisional Application No. 60/852,328, entitled “SYSTEMS AND METHODSFOR STARTUP AND CONTROL OF ELECTRODELESS PLASMA LAMP,” filed Oct. 16,2006. The entire contents of these applications is incorporated hereinby reference.

BACKGROUND

I. Field

The field relates to systems and methods for generating light, and moreparticularly to electrodeless plasma lamps.

II. Background

Electrodeless plasma lamps may be used to provide bright, white lightsources. Because electrodes are not used, they may have longer usefullifetimes than other lamps. In an electrodeless plasma lamp, radiofrequency power may be coupled into a fill in a bulb to create a lightemitting plasma. However, as the fill is ignited and the plasma heatsup, the load conditions of the lamp may change. This can impact thestartup procedure as well as the electronics used to drive the lamp. Inaddition, different modes of operation may require different operatingconditions.

SUMMARY

Example embodiments provide systems and methods for an electrodelessplasma lamp. In some example embodiments, RF power is provided to thelamp body and fill in the bulb at a frequency in the range of betweenabout 50 MHz and about 30 GHz, or any range subsumed therein. In someexamples, the frequency is less than 1 GHz. In an example embodiment,the RF power causes a light emitting plasma discharge in the bulb. Inexample embodiments, RF power is coupled by radiating RF power into alamp body and establishing a standing wave. In some embodiments, RFpower may be provided at or near a resonant frequency for the loadformed by the lamp body, bulb and fill.

In one example embodiment, an RF feed is coupled to the lamp body toprovide power for ignition and steady state operation of the lamp.Feedback is used to adjust frequency in response to changing conditionsof the lamp during startup. A phase shifter is used to adjust the phaseof the power between ignition and steady state operation. A sensor maydetect a lamp operating condition that automatically triggers a shift inphase after the fill in the bulb is vaporized.

In some example embodiments, the phase shift may continue to be adjustedas the plasma heats up and the impedance continues to change. In oneexample, a lookup table is used to store parameters indicating thevoltage to be applied to a phase shifter as the frequency ramps down asthe plasma heats up. In another example, control electronics interpolatea plurality of values to be used for shifting the phase during thisramp.

In some example embodiments, phase is automatically adjusted on aperiodic basis. These phase adjustments may be applied during startupwhen the fill is vaporized, during heat up of the plasma after the fillis vaporized and/or during the run mode of the lamp after the plasma isreaches its full operating temperature. In one example, controlelectronics may automatically adjust the phase to determine the effecton a lamp operating condition, such as the output intensity of the lightor power coupling to the lamp body.

In some example embodiments, the brightness is stabilized after theplasma achieves high brightness. In some example embodiments, the phaseis adjusted to maintain a substantially constant brightness as theplasma heats up after the lamp initially transitions to high brightness.In some embodiments, the brightness is stabilized within 5-20 seconds orless after ignition, even though the load conditions may change as theplasma continues to heat up for several minutes. In some embodiments, alookup table is used to store parameters to control the brightnessduring heat up. In other embodiments, a control parameter isautomatically adjusted in response to detection of a lamp operatingcondition, such as lamp output intensity detected by a photosensor. Insome example embodiments, brightness is quickly stabilized even thoughthe fill may include a metal halide or other material that heats up overa longer period of time and continues to cause changes to the impedanceof the load.

In some example embodiments, impedance matching circuit elements may beswitched into or out of a lamp drive circuit to adjust to changing loadconditions. In one example, a capacitive element may be switched out ofthe circuit after lamp startup. In another aspect, a variable-impedancematching circuit element may be adjusted based on changing loadconditions. In one example, a variable capacitor may be adjusted betweenstartup and run mode. In some embodiments, these aspects may be used toprovide better impedance matching and improved power coupling duringstartup and run mode even though the load conditions change.

In some example embodiments, an amplifier may be operated usingdifferent gate bias voltages during different operating modes of thelamp. The bias condition of the amplifier has a large impact on DC-RFefficiency.

In some example embodiments, the operating class of an amplifier may beselected for different operating modes of a lamp based on a desiredtrade-off between efficiency and dynamic range. For example, anamplifier biased to operate in Class C mode is more efficient than anamplifier biased to operate in Class B mode, which in turn is moreefficient than an amplifier biased to operate in Class A/B mode.However, an amplifier biased to operate in Class NB mode has a betterdynamic range than an amplifier biased to operate in Class B mode, whichin turn has better dynamic range than an amplifier biased to operate inClass C mode.

In some example embodiments, when the lamp is first turned on, theamplifier is biased in a Class MB mode. Class A/B provides betterdynamic range and more gain to allow the amplifier to ignite the plasmaand to adjust to the changing load conditions during startup. Once theplasma reaches its steady state operating condition, the amplifier maybe biased in Class C mode. This provides improved efficiency.

In some example embodiments, the operating class of the amplifier ischanged after startup in response to changes in a lamp operatingcondition. In one example, the operating class of the amplifier ischanged from Class C mode to Class A/B mode or Class B mode if thebrightness of the lamp is modulated below a certain threshold level. Inone example the threshold is between 50-80% of full brightness or anyrange subsumed therein.

In some example embodiments, control electronics provide a gate biasvoltage to an amplifier to control the operating class of the amplifier.The control electronics is responsive to lamp operating conditions tochange the operating class of the amplifier. In one example, the controlelectronics is responsive to an optical sensor or RF power sensorindicating that the plasma has reached high brightness. In anotherexample, the control electronics is responsive to a brightness controlsignal. In example embodiments, the gate bias voltage may be adjustedduring operation of the lamp to change the class of the amplifier. Inother embodiments, the gate bias voltage may be adjusted duringoperation of the lamp to enhance efficiency even if the class of theamplifier is not changed. For example, the gate bias applied to a classD, E or F may be adjusted to enhance efficiency without changing theclass of the amplifier.

In some example embodiments, the lamp body includes a solid dielectricbody with an electrically conductive coating. In example embodiments,power is coupled from the lamp body to the bulb through an uncoateddielectric surface adjacent to the bulb. In example embodiments, thesurface area through which power is coupled to the bulb is relativelysmall. In some embodiments, the surface area is in the range of about5%-50% of the outer surface area of the bulb or any range subsumedtherein. In some embodiments, the surface area is less than 100 mm². Inother examples, the surface area is less than 75 mm², 50 mm² or 35 mm².In some embodiments, the surface area is disposed symmetrically around amiddle region of the bulb and is spaced apart from the ends of the bulb.In some embodiments, this allows power to be concentrated in a narrowregion in the middle of the bulb and a small arc length is formed thatdoes not impinge on the ends of the bulb.

In some example embodiments, the interior of the bulb has a volume inthe range of about 10 mm³ to 750 mm³ or any range subsumed therein. Insome examples, the bulb has an interior volume of less than about 100mm³ or less than about 50 mm³

In some example embodiments, the lamp body has a thin region adjacent toa bulb. In example embodiments, power is concentrated in the thin regionof the lamp body. In some embodiments the thin region has a thickness ofless than 5 mm. In some embodiments, the thin region has a thicknessless than the length of the bulb. In some embodiment, the thin region isbounded by an electrically conductive material on opposing sides. Insome embodiments, the thin region with electrically conductive coatingsprovides a high capacitance that concentrates power near the bulb. Insome embodiments, this is the region of the lamp body with the highestcapacitance.

In some example embodiments, the thin region forms a shelf between thebulb and a substantially thicker region of the lamp body. In someexamples, the length of the shelf between the thicker region of the lampbody and the bulb is less than about 1-5 mm or any range subsumedtherein. In some embodiments, the distance is in the range of about 1-2mm.

In some example embodiments, a gap is formed between the shelf and thebulb. In some embodiments, the gap is filled with a dielectric materialhaving a lower thermal conductivity than the lamp body. In someembodiments, the gap is less than about 1 mm. In some embodiments, thegap is in the range of about ⅛ to 1 mm or any range subsumed therein. Insome embodiments, the gap is less than about 0.5 mm.

In some example embodiments, a drive probe is inserted into the lampbody a distance that is more than 80% of the distance through the lampbody. In some embodiments, the probe extends more than 90% or 95% of thedistance through the lamp body. In some embodiments, the end of theprobe is a distance from a surface of the lamp body in the range ofabout 1-5 mm or any range subsumed therein. In some embodiments, thediameter of the probe is increased to improve coupling so the probe canbe kept further from the surface of the lamp body. In some embodiments,the diameter of the probe is in the range of about 1-5 mm or any rangesubsumed therein. In some embodiments, the diameter of the probe isgreater than 1.5 mm or 2 mm. In some embodiments, the diameter of theprobe is within a range of about +/−50% (or any range subsumed therein)of the distance between the end of the probe and the surface of the lampbody. In some embodiments, the diameter of the probe is about 2 mm andthe distance between the end of the probe and the surface of the lampbody is about 2-3 mm or any range subsumed therein.

In another aspect, an end of the bulb protrudes outside of the lamp bodyby a distance that is greater than the thickness of at least one regionof the lamp body. In some embodiments, at least one end of the bulbprotrudes outside of the lamp body by at least 3-5 mm or more.

In another aspect, the shortest distance between an end of a bulb and adrive probe traverses at least one electrically conductive material in alamp body. In some embodiments, the electrically conductive surface isspaced apart from the bulb and the drive probe. In some embodiments, thedistance between an end of a bulb and a drive probe is less than 5-10 mmor any range subsumed therein. In some embodiments, this distance isless than about 8 mm. In some embodiments, this distance is greater thanthe distance from the end of the probe to a side of the bulb. In someembodiments, a dielectric material between the drive probe and theelectrically conductive material has a higher thermal conductivity thana dielectric material between the bulb and the electrically conductivematerial. In some embodiments, the electrically conductive material is ametallic coating on a waveguide surface.

In another aspect, the shortest distance between an end of a bulb and afeedback probe traverses at least one electrically conductive materialin a lamp body.

In some embodiments, the drive probe has a length in the lamp body thatis in the range of about 10-30 mm or any range subsumed therein or more,the feedback probe has a length in the lamp body that is in the range of0-10 mm or any range subsumed therein or less, and the bulb has a lengthof from about 5-15 mm or any range subsumed therein.

In some embodiments, the shortest distance between the end of a feedbackprobe and the closest point on the drive probe traverses one or moreelectrically conductive surfaces that are spaced apart from the feedbackprobe and drive probe. In some embodiments, the distance from themid-point of the drive probe to the electrically conductive material isless than 1-5 mm or any range subsumed therein. In some embodiments,these surfaces are metallic surfaces of a waveguide body.

In some embodiments, the shortest distance from a mid-point on a driveprobe to the central axis of a lamp body is in the range of about 1-15mm or any range subsumed therein. In some embodiments, this distance isless than 8-10 mm. In some embodiments, this distance traverses anelectrically conductive material. In some embodiments, the electricallyconductive material is a metallic surface of a waveguide body.

In some embodiments, a line segment transverse to, and passing throughthe mid-point of, the drive probe may be defined between a point on acentral axis of the lamp body and an outer surface of the lamp body. Inexample embodiments, the outer surface of the lamp body comprises ametallic waveguide surface. In example embodiments, the distance alongthis line from the central axis to the drive probe is less than thedistance from the drive probe to the outer surface. In some embodiments,the distance from the central axis is 40% or less of the distance fromthe axis to the outer surface. In some embodiments, the distance fromthe drive probe to the outer surface is more than 8-15 mm or any rangesubsumed therein. In some embodiments, the length of the drive probe islonger than the distance between the drive probe and the outer surface.In some embodiments, the length of the drive probe is longer than thedistance between the drive probe and the outer surface.

In each of the above examples, the lamp body may be configured tooperate at an RF power frequency of about 1 GHz or less in someembodiments. In some embodiments, the lamp may operate at an RF powerfrequency of less than about 900 MHz. In some embodiments, the lamp mayoperate at an RF power frequency of between about 100 MHz to 1 GHz orany range subsumed therein.

In some embodiments, the relative permittivity is in the range of about9-15 or any range subsumed therein, the frequency of the RF power isless than about 1 GHz and the volume of the lamp body is in the range ofabout 10 cm³ to 30 cm³ or any range subsumed therein. In one example,the relative permittivity is less than 10, the frequency is less than 1GHz and the volume of the lamp body is less than 30 cm³.

In some embodiments, the relative permittivity is in the range of about9-15 or any range subsumed therein, the frequency of the RF power isless than about 2.5 GHz and the volume of the lamp body is in the rangeof about 4 cm³ to 7 cm³ or any range subsumed therein. In one example,the relative permittivity is less than 10, the frequency is less than2.5 GHz and the volume of the lamp body is less than 7 cm³.

It is understood that each of the above aspects of example embodimentsmay be used alone or in combination with other aspects described aboveor in the detailed description below. A more complete understanding ofexample embodiments and other aspects and advantages thereof will begained from a consideration of the following description read inconjunction with the accompanying drawing figures provided herein. Inthe figures and description, numerals indicate the various features ofexample embodiments, like numerals referring to like features throughoutboth the drawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-section and schematic view of a plasma lamp accordingto an example embodiment.

FIG. 1B is a perspective cross section view of a lamp body with acylindrical outer surface according to an example embodiment.

FIG. 1C is a perspective cross section view of a lamp body with arectangular outer surface according to an alternative exampleembodiment.

FIG. 2A is a flow chart of a method for starting an electrodeless plasmalamp according to an example embodiment.

FIG. 2B illustrates the startup of a lamp using a fill according to anexample embodiment.

FIG. 3 is a flow chart of a method for starting an electrodeless plasmalamp with a Noble gas, Mercury and metal halide fill according to anexample embodiment.

FIG. 4 is a block diagram of control electronics for an electrodelessplasma lamp according to an example embodiment.

FIG. 5A is a block diagram of a method for automatically adjusting thephase of a feedback loop for an electrodeless plasma lamp according toan example embodiment.

FIG. 5B is a flow chart of a method for changing the operating class ofan amplifier according to an example embodiment.

FIG. 6A is a block diagram of a lamp and drive circuit with a switchedcapacitor.

FIG. 6B is a flow chart of a method for starting a lamp using a switchedcapacitor.

FIG. 7A is a block diagram of a lamp and drive circuit with a variablecapacitor.

FIG. 7B is a flow chart of a method for starting a lamp using a variablecapacitor.

DETAILED DESCRIPTION

While the present invention is open to various modifications andalternative constructions, the embodiments shown in the drawings will bedescribed herein in detail. It is to be understood, however, there is nointention to limit the invention to the particular forms disclosed. Onthe contrary, it is intended that the invention cover all modifications,equivalences and alternative constructions falling within the spirit andscope of the invention as expressed in the appended claims.

FIG. 1A is a cross-section and schematic view of a plasma lamp 100according to an example embodiment. In example embodiments, the plasmalamp may have a lamp body 102 formed from one or more solid dielectricmaterials and a bulb 104 positioned adjacent to the lamp body. The bulbcontains a fill that is capable of forming a light emitting plasma. Alamp drive circuit 106 couples radio frequency power into the lamp body102 which, in turn, is coupled into the fill in the bulb 104 to form thelight emitting plasma. In example embodiments, the lamp body 102 forms awaveguide that contains and guides the radio frequency power. In exampleembodiments, the radio frequency power may be provided at or near afrequency that resonates within the lamp body 102.

Lamp 100 has a drive probe 120 inserted into the lamp body 102 toprovide radio frequency power to the lamp body 102. In the example ofFIG. 1A, the lamp also has a feedback probe 122 inserted into the lampbody 102 to sample power from the lamp body 102 and provide it asfeedback to the lamp drive circuit 106.

A lamp drive circuit 106 including a power supply, such as amplifier124, may be coupled to the drive probe 120 to provide the radiofrequency power. The amplifier 124 may be coupled to the drive probe 120through a matching network 126 to provide impedance matching. In anexample embodiment, the lamp drive circuit 106 is matched to the load(formed by the lamp body, bulb and plasma) for the steady stateoperating conditions of the lamp. The lamp drive circuit 106 is matchedto the load at the drive probe 120 using the matching network 126.

In example embodiments, radio frequency power may be provided at afrequency in the range of between about 50 MHz and about 10 GHz or anyrange subsumed therein. The radio frequency power may be provided todrive probe 120 at or near a resonant frequency for lamp body 102. Thefrequency may be selected based on the dimensions, shape and relativepermittivity of the lamp body 102 to provide resonance in the lamp body102. In example embodiments, the frequency is selected for a fundamentalresonant mode of the lamp body 102, although higher order modes may alsobe used in some embodiments. In example embodiments, the RF power may beapplied al a resonant frequency or in a range of from 0% to 10% above orbelow the resonant frequency or any range subsumed therein. In someembodiments, RF power may be applied in a range of from 0% to 5% aboveor below the resonant frequency. In some embodiments, power may beprovided at one or more frequencies within the range of about 0 to 50MHz above or below the resonant frequency or any range subsumed therein.In another example, the power may be provided at one or more frequencieswithin the resonant bandwidth for at least one resonant mode. Theresonant bandwidth is the full frequency width at half maximum of poweron either side of the resonant frequency (on a plot of frequency versuspower for the resonant cavity).

In example embodiments, the radio frequency power causes a lightemitting plasma discharge in the bulb. In example embodiments, power isprovided by RF wave coupling. In example embodiments, RF power iscoupled at a frequency that forms a standing wave in the lamp body(sometimes referred to as a sustained waveform discharge or microwavedischarge when using microwave frequencies). In other embodiments, acapacitively coupled or inductively coupled electrodeless plasma lampmay be used. Other high intensity discharge lamps may be used in otherembodiments.

In some example embodiments, the amplifier 124 may be operated inmultiple operating modes at different bias conditions to improvestarting and then to improve overall amplifier efficiency during steadystate operation. The bias condition of the amplifier 124 has a largeimpact on DC-RF efficiency. Amplifiers are classified based on theirconduction angles. Class A amplifiers have a conduction angle of 360° or2π and use 100% of the input signal. However, Class A amplifiers are notvery efficient. Class A/B amplifiers have a conduction angle of 181° to359° (π<a<2π). More than 50% but less than 100% of the input signal isused. Class B amplifiers have a conduction angle of 180° or π. 50% ofthe input signal is used. Class C amplifiers have a conduction angle of0° to 179° (a<π). Less than 50% of the input signal is used. As aresult, an amplifier biased to operate in Class C mode is more efficientthan an amplifier biased to operate in Class B mode, which in turn ismore efficient than an amplifier biased to operate in Class A/B mode.However, an amplifier biased to operate in Class A/B mode has a betterdynamic range than an amplifier biased to operate in Class B mode, whichin turn has better dynamic range than an amplifier biased to operate inClass C mode.

In one example, the amplifier may be biased to operate in Class A/B modeto provide better dynamic range during startup and in Class C modeduring steady state operation to provide more efficiency. In anotherexample, the amplifier may be switched back to Class A/B mode forcertain modes of operation where the brightness of the lamp is modulatedbelow a threshold level (e.g., 70%).

In other embodiments, the gate bias voltage may be adjusted duringoperation of the lamp to enhance efficiency even if the class of theamplifier is not changed. For example, the gate bias applied to a classD, E or F may be adjusted to enhance efficiency without changing theclass of the amplifier.

The amplifier may also have a gain control that can be used to adjustthe gain of the amplifier 124. Amplifier 124 may include either aplurality of gain stages or a single stage.

The feedback probe 122 is coupled to the input of the amplifier 124through an attenuator 128 and phase shifter 130. The attenuator 128 isused to adjust the power of the feedback signal to an appropriate levelfor input to the phase shifter 130. In some embodiments, a secondattenuator may be used between the phase shifter 130 and the amplifier124 to adjust the power of the signal to an appropriate level foramplification by the amplifier 124. In some embodiments, theattenuator(s) may be variable attenuators controlled by the controlelectronics 132. In other embodiments, the attenuators may be set to afixed value. In some embodiments, the lamp drive circuit may not includean attenuator. In an example embodiment, the phase shifter 130 may be avoltage-controlled phase shifter controlled by the control electronics132.

The feedback loop automatically oscillates at a frequency based on theload conditions and phase of the feedback signal. This feedback loop maybe used to maintain a resonant condition in the lamp body. 102 eventhough the load conditions change as the plasma is ignited and thetemperature of the lamp changes. If the phase is such that constructiveinterference occurs for waves of a particular frequency circulatingthrough the loop, and if the total response of the loop (including theamplifier, lamp, and all connecting elements) at that frequency is suchthat the wave is amplified rather than attenuated after traversing theloop, the loop will oscillate at that frequency. Whether a particularsetting of the phase-shifter induces constructive or destructivefeedback depends on frequency. The phase-shifter 128 can be used tofinely tune the frequency of oscillation within the range supported bythe lamp's frequency response. In doing so, it also effectively tuneshow well RF power is coupled into the lamp because power absorption isfrequency-dependent. Thus, the phase-shifter 130 provides fast,finely-tunable control of the lamp output intensity. Both tuning anddetuning are useful. For example: tuning can be used to maximizeintensity as component aging changes the overall loop phase; detuningcan be used to control lamp dimming. In some example embodiments, thephase selected for steady state operation may be slightly out ofresonance, so maximum brightness is not achieved. This may be used toleave room for the brightness to be increased and/or decreased bycontrol electronics 132.

In FIG. 1A, control electronics 132 is connected to attenuator 128,phase shifter 130 and amplifier 124. The control electronics 132 providesignals to adjust the level of attenuation provided by the attenuator128, phase of phase shifter 130, the class in which the amplifier 124operates (e.g., Class A/B, Class B or Class C mode) and/or the gain ofthe amplifier 124 to control the power provided to the lamp body 102. Inone example, the amplifier 124 has three stages, a pre-driver stage, adriver stage and an output stage, and the control electronics 132provides a separate signal to each stage (drain voltage for thepre-driver stage and gate bias voltage of the driver stage and theoutput stage). The drain voltage of the pre-driver stage can be adjustedto adjust the gain of the amplifier. The gate bias of the driver stagecan be used to turn on or turn off the amplifier. The gate bias of theoutput stage can be used to choose the operating mode of the amplifier(e.g., Class A/B, Class B or Class C). Control electronics 132 can rangefrom a simple analog feedback circuit to amicroprocessor/microcontroller with embedded software or firmware thatcontrols the operation of the lamp drive circuit. The controlelectronics 132 may include a lookup table or other memory that containscontrol parameters (e.g., amount of phase shift or amplifier gain) to beused when certain operating conditions are detected. In exampleembodiments, feedback information regarding the lamp's light outputintensity is provided either directly by an optical sensor 134, e.g., asilicon photodiode sensitive in the visible wavelengths, or indirectlyby an RF power sensor 136, e.g., a rectifier. The RF power sensor 136may be used to determine forward power, reflected power or net power atthe drive probe 120 to determine the operating status of the lamp. Adirectional coupler may be used to tap a small portion of the power andfeed it to the RF power sensor 136. An RF power sensor may also becoupled to the lamp drive circuit at the feedback probe 122 to detecttransmitted power for this purpose. In some embodiments, the controlelectronics 132 may adjust the phase shifter 130 on an ongoing basis toautomatically maintain desired operating conditions.

The power to the lamp body 102 and operating class of the amplifier 124may be controlled to provide a desired startup sequence for igniting theplasma. As the plasma ignites and heats up during the startup process,the impedance and operating conditions of the lamp change. In order toprovide for efficient power coupling during steady state operation ofthe lamp, the lamp drive circuit 106 is impedance matched to the steadystate load of the lamp body, bulb and plasma after the plasma is ignitedand reaches steady state operating conditions. This allows power to becritically coupled from the drive circuit 106 to the lamp body 102 andplasma during steady state operation. However, the power from the drivecircuit 106 is overcoupled to the lamp body 102 and plasma at startup.

When the power is initially turn on, the load appears as an open circuitand the power is substantially reflected. However, the gas in the bulbignites and breaks down almost immediately. After ignition, theimpedance is low and much of the power from the drive circuit 106 isreflected. For example, the amplifier 124 may provide about 170 watts offorward power, but more than half of this power may be reflected atstartup. The net power to the lamp may be only between about 40-100watts (or any range subsumed therein) after ignition and prior tosubstantial vaporization of the Mercury and metal halide (when the lamptransitions to high brightness), and the rest may be reflected.

FIG. 2 is a flow chart of an example startup procedure. In someembodiments, the amplifier is biased to operate in Class A/B mode duringstartup. Class A/B provides better dynamic range and more gain to allowthe amplifier to ignite the plasma and to adjust to the changing loadconditions during startup. Power is initially provided to the lamp bodyat or near a resonant frequency and the gas in the bulb 104 ignitesalmost immediately as indicated at 200. After ignition of the gas, theload conditions change and other fill materials in the bulb vaporize andwarm up as shown at 202. Once the fill is vaporized, a bright light isemitted by the plasma. At this point, an operating condition of the lampmay be detected as indicated at 204. For example, the light from thebulb 104 may be detected by a sensor 134 and provided to the controlelectronics 132. Alternatively, a power sensor 136 may be used to detectthe change in lamp operating conditions. When the fill is vaporized, theimpedance changes and the quality factor Q of the cavity drops. When theapplicable change in lamp operating conditions is detected, the phaseshift of the phase shifter 130 may be automatically adjusted toaccommodate for the change in frequency due to the change in theimpedance of the plasma as indicated at 206. As the plasma continues toheat up, the impedance continues to change and the frequency continuesto drop until the lamp reaches steady state operating conditions. As thefrequency changes, the phase of the phase shifter 130 may continue to beadjusted to match the changes in frequency as indicated at 208. Thisramp may take several minutes. In order to avoid a drop in brightness,the control electronics 132 adjusts the phase of the phase shifter 130in stages to match the ramp. In an example embodiment, the controlelectronics 132 may change the voltage applied to the phase shifter 130in equal increments over a set period of time for the ramp, which can bedetermined empirically. As shown at 210, the phase continues to beadjusted until all of the steps in the ramp are completed. While thevalues for the ramp may be selected based on a variety of objectives, inexample embodiments the values are selected to maintain a substantiallyconstant brightness of the lamp as the plasma heats up after highbrightness is initially achieved. This allows brightness to be quicklystabilized even though the load conditions may continue to change as theplasma heats up. In other embodiments, the values may be selected tomaximize power coupling or brightness, to ramp brightness in a desiredway or to achieve other objectives. At the end of the ramp, the plasmahas reached its full operating temperature and the lamp enters itssteady state run mode as shown at 212. In some embodiments, theamplifier may be biased in Class C mode when the lamp enters its steadystate run mode. This provides improved efficiency.

The changes in impedance during the startup procedure depend upon thefill in the bulb. In some example embodiments, a high pressure fill isused to increase the resistance of the gas. This can be used to decreasethe overall startup time required to reach full brightness for steadystate operation. In one example, a noble gas such as Neon, Argon,Krypton or Xenon is provided at high pressures between 200 Torr to 3000Torr or any range subsumed therein. Pressures less than or equal to 760Torr may be desired in some embodiments to facilitate filling the bulbat or below atmospheric pressure. In particular embodiments, pressuresbetween 400 Torr and 600 Torr are used to enhance starting. Example highpressure fills may also include metal halide and Mercury which have arelatively low vapor pressure at room temperature. An ignition enhancersuch as Kr₈₅ may also be used. In a particular example, the fillincludes 1.608 mg Mercury, 0.1 mg Indium Bromide and about 10 nanoCurieof Kr₈₅. In this example, Argon or Krypton is provided at a pressure inthe range of about 400 Torr to 700 Torr, depending upon desired startupcharacteristics. Initial breakdown of the noble gas is more difficult athigher pressure, but the overall warm up time required for the fill tofully vaporize and reach peak brightness is reduced. The above pressuresare measured at 22° C. (room temperature). It is understood that muchhigher pressures are achieved at operating temperatures after the plasmais formed. For example, the lamp may provide a high intensity dischargeat high pressure during operation (e.g., much greater than 2 atmospheresand 10-30 atmospheres or more in example embodiments). These pressuresand fills are examples only and other pressures and fills may be used inother embodiments.

An example startup time for a high pressure fill is illustrated in FIG.2B. In this example, the fill includes Argon at about 400-600 Torr,Mercury and one or more metal halides such as Indium Bromide. As shownin FIG. 2B, the warm up time is short and may be less than 2 seconds insome embodiments. As shown in FIG. 2B, the warm up starts upon ignitionand breakdown of the noble gas and continues until the lamp transitionsto high brightness. FIG. 2B shows the intensity of light output detectedby a photodiode (PD) during startup. In this example, the warm up timeis indicated at a photodiode intensity of about 0.06, which is about 20%of the peak output intensity. The time from ignition to the beginning ofthe transition curve (e.g., around 3-5% of peak intensity) is evenshorter and is slightly over a second in this example. The lamp thentransitions to high brightness. The transition period from warm up to80% peak brightness in this example is about one second. In exampleembodiments, it is believed that ignition time can be reduced to afraction of a second (for example, using increased ignition enhancer)and that higher pressure noble gas can be used to further reduce warm uptime (e.g., to 1-2 seconds or less). As a result, it is believed thatvery fast startup times of 1-3 seconds may be achieved even though thenet power is limited due to the impedance mismatch during startup. FIG.2B is also shows the DC current (Idc) provided by the amplifier. Asshown in FIG. 2B, the DC current may be limited during warm up. This mayhelp reduce the potential for damage to the lamp drive circuit duringperiods of high reflection. After transition (e.g., 80% peak brightness)in this example, the DC current is raised to a higher level. In theexample of FIG. 2E, the DC current is less than 8 Amperes during warm upand more than 8 Amperes during steady state operation, even though theimpedance is substantially lower during warm up (e.g., about 10 ohms)than during steady state (e.g., about 50 ohms). In the example of FIG.2B, once the lamp transitions to high brightness, the light outputintensity of the lamp is quickly stabilized. The phase shift andresulting frequency provided by the lamp drive circuit may be adjustedto maintain a substantially constant brightness even though the loadconditions continue to change as the metal halide heats up over severalminutes. In one example, this is provided by adjusting phase based onpredetermined parameters. In another example, the phase is automaticallyadjusted to maintain a constant brightness in response to a detectedlamp operating condition, such as a light sensor or power sensor. Inexample embodiments, the brightness may be stabilized within 5-20seconds or less, or any range subsumed therein. As shown in FIG. 2B, thebrightness (as indicated by the detected photodiode intensity) issubstantially constant after about 8 seconds even though the metalhalide continues to heat up and load conditions continue to change. Inexample embodiments, the light output intensity may be maintained within+/−1% or less of a constant value during heat up of the plasma. In otherembodiments, the brightness may be stabilized within a range of about0%-3% of a constant value or any range subsumed therein. In exampleembodiments, the brightness during heat up may be stabilized at abrightness in the range of about 80-100% of the maximum peak brightnessthat can be achieved by the lamp or any range subsumed therein. Inexample embodiments, the steady state brightness is slightly below themaximum peak brightness to allow for brightness to be increased tocompensate for aging components or other changes during the lifetime ofthe lamp.

FIG. 3 is a flow chart of an example startup procedure for a fill thatincludes a noble gas, Mercury and metal halide. In one example, the fillincludes 400-600 Torr of Argon, 1.608 mg Mercury, 0.1 mg Indium Bromideand about 10 nanoCurie of Kr₈₅. In this example, the lamp 100 starts ata frequency of about 895 MHz at power on (step 300 in FIG. 3) and theArgon ignites almost immediately (step 302 in FIG. 3). Upon ignition,the frequency drops to about 880 Mhz due to the change in impedance fromthe ignition of the Argon. The frequency is automatically adjusted bythe feedback loop as indicated at 306 in FIG. 3. The Mercury thenvaporizes and heats up as indicated at 308. The Indium Bromide alsovaporizes and light is emitted at high brightness as indicated at 310.When this light is detected by sensor 134, the phase shifter 130 isautomatically adjusted to accommodate for the change in frequency due tothe change in the impedance of the plasma as indicated at 314. In oneexample, the threshold may be triggered by detection of visible lightoutput intensity in the range of from about 20%-90% of peak light outputintensity. In particular examples, 80% or 90% of peak output intensityis used as a threshold. In other examples, the threshold may bedetermined based on forward and/or reflected power detected by the lampdrive circuit. With the appropriate phase shift, the feedback loopadjusts the frequency to about 885 MHz. In an example embodiment, whenthis startup process is used with a high pressure fill as describedabove, the startup process from power on to vaporization of the fill(steps 300 to 314 in FIG. 3) may be completed in about 5-10 seconds orless. As a result, high brightness can be achieved very rapidly.

As the plasma continues to heat up, the impedance continues to changeand the frequency continues to drop until the lamp reaches steady stateoperating conditions. In example embodiments, the impedance after warmup is in the range of 40-60 ohms or any range subsumed therein. In aparticular embodiment, the impedance is about 50 ohms during steadystate operation. As the frequency changes, the phase of the phaseshifter 130 may continue to be adjusted to match the changes infrequency. In an example startup procedure, the frequency ramps down toa steady state operating frequency of about 877 MHz. This ramp may takeseveral minutes. In order to avoid a drop in brightness, the controlelectronics 132 adjusts the phase of the phase shifter 130 in stages tomatch the ramp. As shown in FIG. 4, a lookup table 406 in the controlelectronics 132 may be used to store a sequence of parameters indicatingthe amount of phase shift to be used by the control electronics 132during the startup procedure. In one example, the voltage to be appliedto the phase shifter is stored in the lookup table for startup(ignition), high (e.g., 80-90% of peak) brightness of the plasma (lightmode) and steady state after the lamp is heated (run mode). Amicroprocessor 402 in control electronics 132 may use these parametersto shift the phase in increments between the time that transition tohigh brightness is detected and completion of heat up. In one example,firmware executed by the microprocessor 402 linearly interpolate betweenthe desired phase at full vaporization (light mode) when the frequencyis about 885 MHz and the desired phase at the end of heat up (run mode)when the frequency is about 877 MHz. In one example, firmware in thecontrol electronics linearly interpolates sixteen values for the phasevoltage that are applied in equal increments over a period of about 5minutes as the lamp ramps from light mode to run mode. The phaseadjustments and ramp may be determined empirically and programmed intothe lookup table based on the operating conditions of the particularlamp. In order to adjust the phase, the microprocessor 402 outputs avoltage signal on a control line 410 which is connected to the phaseshifter 130 (other control lines provided by the control electronics maybe used to control the attenuator 128 and the amplifier 124). The phaseadjustments continue in sequence until the ramp is complete as indicatedat 318 in FIG. 3.

In an alternative embodiment, the control electronics 132 mayautomatically shift the phase periodically to determine whether a changein one direction or another results in more efficient power couplingand/or higher brightness (based on feedback from an optical sensor or rfpower sensor in the drive circuit). This periodic phase shift can beperformed very rapidly, so an observer does not notice any visiblechange in the light output intensity. FIG. 5A is a flow chartillustrating an example method for automatically adjusting the phase.This process may be performed during startup, during ramp of thefrequency or during steady state operation of the lamp as desired. Asshown at 500 the control electronics detects a lamp operating condition.For example, the control electronics may receive a signal from sensor134 indicating the intensity of the light output or a measurement fromRF power detector 136. In example embodiments, the light outputintensity detected by light sensor 134 may be repeatedly checked by thecontrol electronics 132 to determine whether there has been a change inbrightness. This may be checked more than once every second and in someembodiments may be checked every 300 microseconds. In some embodiments,this can be used during ramp down of frequency as the plasma heats up.In other embodiments, this can be used for brightness lock to ensureconsistent brightness over the lifetime of the lamp, even if aging ofcomponents introduces changes. In some embodiments, this can also beused for brightness control. If the lamp condition is not at the desiredlevel, the control electronics 132 then shifts the phase of the phaseshifter in a small increment as indicated at 504. The direction may bedetermined based on the expected conditions for the particular mode ofoperation (e.g., based on an expectation that the frequency will rampdown during heat up of the plasma). The lamp operating condition is thenmeasured again as indicated at 506. If the shift resulted in a desiredchange as indicated at step 506 (e.g., the brightness increased), thenthe control electronics continues to adjust the phase shift in smallincrements in the same direction (see step 510). If the shift did notresult in a desired change (e.g., the brightness decreased), then thecontrol electronics 132 may try shifting the phase in the oppositedirection as indicated at step 518. As shown at steps 510, 512 and 514,the phase continues to be adjusted in small increments so long as thelamp operating condition continues to improve. Once the lamp operatingcondition is no longer improved, the phase is shifted back one incrementto optimum level as indicated at step 516. In some embodiments, thecontrol electronics 132 may then wait a set period of time beforerepeating the automatic phase adjustment procedure.

The phase of the phase shifter 130 and/or gain of the amplifier 124 mayalso be adjusted after startup to change the operating conditions of thelamp. For example, the power input to the plasma in the bulb 104 may bemodulated to modulate the intensity of light emitted by the plasma. Thiscan be used for brightness lock to maintain a constant brightness evenif components age. This can also be used for brightness adjustment. Ifthe lamp is not operating at resonance for peak brightness, the phasemay be shifted to increase brightness. The phase may also be shifted todim the lamp. In some embodiments, the lamp may be adjusted to 20% to100% of peak brightness, or any range subsumed therein, whilemaintaining continuous supply of power to the lamp and withoutextinguishing the plasma discharge. In some embodiments, this may beaccomplished by changing the phase shift without changing the voltagelevel that controls the gain of the amplifier. In other embodiments, thegain of the amplifier may also be adjusted. The light output intensityof the lamp may also be modulated to adjust for video effects in aprojection display. For example, a projection display system may use amicrodisplay that controls intensity of the projected image usingpulse-width modulation (PWM). PWM achieves proportional modulation ofthe intensity of any particular pixel by controlling, for each displayedframe, the fraction of time spent in either the “ON” or “OFF” state. Byreducing the brightness of the lamp during dark frames of video, alarger range of PWM values may be used to distinguish shades within theframe of video. This mode of operation is referred to as “Dynamic Dark”.The brightness of the lamp may also be modulated during particular colorsegments of a color wheel for color balancing or to compensate for greensnow effect in dark scenes by reducing the brightness of the lamp duringthe green segment of the color wheel.

In another example, the phase shifter 130 can be modulated to spread thepower provided by the lamp circuit 106 over a larger bandwidth. This canreduce ElectroMagnetic Interference (EMI) at any one frequency andthereby help with compliance with FCC regulations regarding EMI. Inexample embodiments, the degree of spectral spreading may be from 5-30%or any range subsumed therein. In one example, the control electronics132 may include circuitry to generate a sawtooth voltage signal and sumit with the control voltage signal to be applied to the phase shifter130. In another example, the control electronics 132 may include amicrocontroller that generates a Pulse Width Modulated (PWM) signal thatis passed through an external low-pass filter to generate a modulatedcontrol voltage signal to be applied to the phase shifter 130. Inexample embodiments, the modulation of the phase shifter 130 can beprovided at a level that is effective in reducing EMI without anysignificant impact on the plasma in the bulb.

In example embodiments, the amplifier 124 may be operated at differentbias conditions during different modes of operation for the lamp. FIG.5B is a flow chart showing an example method for changing the operatingclass of the amplifier during operation of the lamp. As shown in FIG.5B, the lamp starts at step 550. At startup, the amplifier is in ClassA/B mode as indicated at 552. At step 554, the control electronics 132determines whether the plasma has ignited and is ready to enter runmode. The control electronics 132 may determine when the plasma achievesa threshold brightness based on inputs from optical sensor 134 or RFpower sensor 136. The control electronics may be configured to wait apredetermined time after high brightness is achieved to allow forcompletion of heat up of the plasma before entering run mode. The lampthen enters run mode as indicated at step 556.

In this example, the control electronics is configured to switch theoperating class of the amplifier 124 during Dynamic Dark mode when thebrightness drops below a threshold level. As shown at step 558, thecontrol electronics 132 checks whether the lamp is in Dynamic Dark mode.The control electronics are configured to enter Dynamic Dark mode whenparticular characteristics are detected in a video frame indicating thatthe lamp brightness can be reduced to enhance the dynamic range (e.g.,based on mean brightness, maximum brightness, or other characteristicsor combinations of characteristics). If the lamp is not in Dynamic Darkmode, the amplifier is changed to Class C mode as indicated at step 560and remains in Class C mode until Dynamic Dark is detected. If the lampis in Dynamic Dark mode, the control electronics determines whether thereduction in brightness for Dynamic Dark will cause the brightness todrop below a threshold level. In one example, the threshold is 70% offull brightness. In other examples, this threshold may range from 50-80%of full brightness or any range subsumed therein. If the brightness willdrop below the threshold, the control electronics changes the bias tocause the amplifier 124 to operate in Class A/B mode as indicated at564. This provides for greater dynamic range to accommodate the changein brightness. Otherwise the amplifier remains in Class C mode asindicated at 566, which provides better efficiency. The brightness levelis then adjusted as shown at step 568. The process is then repeated asindicated at 558. This is an example only and amplifier bias may beadjusted in response to other lamp operating modes or lamp operatingconditions. For example, the bias may be adjusted any time that thebrightness of the lamp will drop below a threshold level (for example, athreshold in the rang of from about 20%-90% of peak brightness).

FIG. 4 is a block diagram showing example control electronics for thephase shifter 130 and amplifier 124 of lamp drive circuit 106. In theexample of FIG. 4, the microprocessor 402 provides three control signalsto amplifier 124. In this example, the amplifier 124 has three stages, apre-driver stage 124 a, a driver stage 124 b and an output stage 124 c,and the control electronics 132 provides a separate signal to each stage(drain voltage signal 412 for the pre-driver stage 124 a, gate biasvoltage signal 414 for the driver stage 124 b and gate bias voltagesignal 416 for the output stage 124 c). The drain voltage of thepre-driver stage 124 a can be adjusted to adjust the gain of theamplifier. The gate bias of the driver stage 124 b can be used to turnon or turn off the amplifier. The gate bias of the output stage 124 ccan be used to choose the operating mode of the amplifier (e.g., ClassA/B, Class B or Class C). In some embodiments, these signals may passthrough other circuitry before being applied to the amplifier 124.

In one example, the control electronics 132 puts the amplifier 124 inClass A/B mode by applying a gate bias voltage signal 416 of about 4volts to the output stage 124 c. This turns the transistors in theoutput stage 124 c slightly on, so they draw some current and have anconduction angle greater than 180°. The bias is removed (signal 416 ischanged to 0 volts) to put the amplifier in Class C mode with aconduction angle of less than 180°. In embodiments using Class B mode, agate bias signal 416 of about 3.4 volts is applied to the output stage124 c. This does not draw any current, but is at the borderline (with aconduction angle of about)180°. The microprocessor 402 receives one ormore input signals 408 that can be used to determine lamp operatingconditions and the mode of operation of the lamp. These input signalscan be used by the microprocessor 402 to determine the desired operatingclass for the amplifier 124 and the appropriate gate bias voltage toassert on line 416. Inputs may include inputs from optical sensor 134,RF power sensor 136 or inputs from video processing circuitry or otherparts of the system (e.g., to determine whether to use Dynamic Dark modeor other mode of operation).

Additional aspects of electrodeless plasma lamps according to exampleembodiments will now be described with reference to FIGS. 1A, 1B and 1C.In example embodiments, the lamp body 102 has a relative permittivitygreater than air. The frequency required to excite a particular resonantmode in the lamp body 102 generally scales inversely to the square rootof the relative permittivity (also referred to as the dielectricconstant) of the lamp body. As a result, a higher relative permittivityresults in a smaller lamp body required for a particular resonant modeat a given frequency of power. The shape and dimensions of the lamp body102 also affect the resonant frequency as described further below. In anexample embodiment, the lamp body 102 is formed from solid aluminahaving a relative permittivity of about 9.2. In some embodiments, thedielectric material may have a relative permittivity in the range offrom 2 to 100 or any range subsumed therein, or an even higher relativepermittivity. In some embodiments, the body may include more than onesuch dielectric material resulting in an effective relative permittivityfor the body within any of the ranges described above. The body may berectangular, cylindrical or other shape as described further below.

In example embodiments, the outer surfaces of the lamp body 102 may becoated with an electrically conductive coating 108, such aselectroplating or a silver paint or other metallic paint which may befired onto the outer surface of the lamp body. The electricallyconductive material 108 may be grounded to form a boundary condition forthe radio frequency power applied to the lamp body 102. The electricallyconductive coating helps contain the radio frequency power in the lampbody. Regions of the lamp body may remain uncoated to allow power to betransferred to or from the lamp body. For example, the bulb 104 may bepositioned adjacent to an uncoated portion of the lamp body to receiveradio frequency power from the lamp body.

In the example embodiment of FIG. 1A, an opening 110 extends through athin region 112 of the lamp body 102. The surfaces 114 of the lamp body102 in the opening 110 are uncoated and at least a portion of the bulb104 may be positioned in the opening 110 to receive power from the lampbody 102. In example embodiments, the thickness H2 of the thin region112 may range from 1 mm to 10 mm or any range subsumed therein and maybe less than the outside length and/or interior length of the bulb. Oneor both ends of the bulb 104 may protrude from the opening 110 andextend beyond the electrically conductive coating 108 on the outersurface of the lamp body. This helps avoid damage to the ends of thebulbs from the high intensity plasma formed adjacent to the region wherepower is coupled from the lamp body. In other embodiments, all or aportion of the bulb may be positioned in a cavity extending from anopening on the outer surface of the lamp body and terminating in thelamp body. In other embodiments, the bulb may be positioned adjacent toan uncoated outer surface of the lamp body or in a shallow recess formedon the outer surface of the waveguide body. In some example embodiments,the bulb may be positioned at or near an electric field maxima for theresonant mode excited in the lamp body.

The bulb 104 may be quartz, sapphire, ceramic or other desired bulbmaterial and may be cylindrical, pill shaped, spherical or other desiredshape. In one example embodiment, the bulb is cylindrical in the centerand forms a hemisphere at each end. In one example, the outer length(from tip to tip) is about 15 mm and the outer diameter (at the center)is about 5 mm. In this example, the interior of the bulb (which containsthe fill) has an interior length of about 9 mm and an interior diameter(at the center) of about 2.2 mm. The wall thickness is about 1.4 mmalong the sides of the cylindrical portion and about 2.25 mm at thefront end and about 3.75 mm on the other end. In this example, theinterior bulb volume is about 31.42 mm³. In other example embodiments,the bulb may have an interior width or diameter in a range between about2 and 30 mm or any range subsumed therein, a wall thickness in a rangebetween about 0.5 and 4 mm or any range subsumed therein, and aninterior length between about 2 and 30 mm or any range subsumed therein.In example embodiments, the interior bulb volume may range from 10 mm³and 750 mm³ or any range subsumed therein. These dimensions are examplesonly and other embodiments may use bulbs having different dimensions.

In example embodiments, the bulb 104 contains a fill that forms a lightemitting plasma when radio frequency power is received from the lampbody 102. The fill may include a noble gas and a metal halide. Additivessuch as Mercury may also be used. An ignition enhancer may also be used.A small amount of an inert radioactive emitter such as Kr₈₅ may be usedfor this purpose. In other embodiments, different fills such as Sulfur,Selenium or Tellurium may also be used. In some examples, a metal halidesuch as Cesium Bromide may be added to stabilize a discharge of Sulfur,Selenium or Tellurium. As described above, some embodiments may use ahigh pressure fill to enhance starting.

A layer of material 116 may be placed between the bulb 104 and thedielectric material of lamp body 102. In example embodiments, the layerof material 116 may have a lower thermal conductivity than the lamp body102 and may be used to optimize thermal conductivity between the bulb104 and the lamp body 102. In an example embodiment, the layer 116 mayhave a thermal conductivity in the range of about 0.5 to 10watts/meter-Kelvin (W/mK) or any range subsumed therein. For example,alumina powder with 55% packing density (45% fractional porosity) andthermal conductivity in a range of about 1 to 2 watts/meter-Kelvin(W/mK) may be used. In some embodiments, a centrifuge may be used topack the alumina powder with high density. In an example embodiment, alayer of alumina powder is used with a thickness D5 within the range ofabout ⅛ mm to 1 mm or any range subsumed therein. Alternatively, a thinlayer of a ceramic-based adhesive or an admixture of such adhesives maybe used. Depending on the formulation, a wide range of thermalconductivities is available. In practice, once a layer composition isselected having a thermal conductivity close to the desired value,fine-tuning may be accomplished by altering the layer thickness. Someexample embodiments may not include a separate layer of material aroundthe bulb and may provide a direct conductive path to the lamp body.Alternatively, the bulb may be separated from the lamp body by anair-gap (or other gas filled gap) or vacuum gap.

In some example embodiments, alumina powder or other material may alsobe packed into a recess 118 formed below the bulb 104. In the exampleshown in FIG. 1A, the alumina powder in the recess 118 is outside theboundaries of the waveguide formed by the electrically conductivematerial 108 on the surfaces of the lamp body 102. The material in therecess 118 provides structural support, reflects light from the bulb andprovides thermal conduction. One or more heat sinks may also be usedaround the sides and/or along the bottom surface of the lamp body tomanage temperature. Thermal modeling may be used to help select a lampconfiguration providing a high peak plasma temperature resulting in highbrightness, while remaining below the working temperature of the bulbmaterial. Example thermal modeling software includes the TAS softwarepackage available commercially from Harvard Thermal, Inc. of Harvard,Mass.

In an example embodiment, the probes 120 and 122 may be brass rods gluedinto the lamp body using silver paint. In other embodiments, a sheath orjacket of ceramic or other material may be used around the bulbs, whichmay change the coupling to the lamp body. In an example embodiment, aprinted circuit board (pcb) may be positioned transverse to the lampbody for the drive electronics. The probes 120 and 122 may be solderedto the pcb and extend off the edge of the pcb into the lamp body(parallel to the pcb and orthogonal to the lamp body). In otherembodiments, the probes may be orthogonal to the pcb or may be connectedto the lamp drive circuit through SMA connectors or other connectors. Inan alternative embodiment, the probes may be provided by a pcb trace andportions of the pcb board containing the trace may extend into the lampbody. Other radio frequency feeds may be used in other embodiments, suchas microstrip lines or fin line antennas.

In an example embodiment, the drive probe 120 is positioned closer tothe bulb in the center of the lamp body than the electrically conductivematerial 108 around the outer circumference of the lamp body 102. Thispositioning of the drive prove 120 can be used to improve coupling ofpower to the plasma in the bulb 104.

An amplifier 124 is used to provide radio frequency power to the driveprobe 120. A high efficiency amplifier may have some unstable regions ofoperation. The amplifier 124 and phase shift imposed by the feedbackloop of the lamp circuit 106 should be configured so that the amplifieroperates in stable regions even as the load condition of the lampchanges. The phase shift imposed by the feedback loop is determined bythe length of the loop (including matching network 126) and any phaseshift imposed by circuit elements such as a phase shifter 130. Atinitial startup before the noble gas in the bulb is ignited, the loadappears to the amplifier as an open circuit. The load characteristicschange as the noble gas ignites, the fill vaporizes and the plasma heatsup to steady state operating conditions. The amplifier and feedback loopare designed so the amplifier will operate within stable regions acrossthe load conditions that may be presented by the lamp body, bulb andplasma. The amplifier 124 may include impedance matching elements suchas resistive, capacitive and inductive circuit elements in series and/orin parallel. Similar elements may be used in the matching network. Inone example embodiment, the matching network is formed from a selectedlength of pcb trace that is included in the lamp drive circuit betweenthe amplifier 124 and the drive probe 120. These elements are selectedboth for impedance matching and to provide a phase shift in the feedbackloop that keeps the amplifier within stable regions of its operation. Aphase shifter 130 may be used to provide additional phase shifting asneeded to keep the amplifier in stable regions.

The amplifier 124 and phase shift in the feedback loop may be designedby looking at the reflection coefficient Γ, which is a measure of thechanging load condition over the various phases of lamp operation,particularly the transition from cold gas at start-up to hot plasma atsteady state. Γ, defined with respect to a reference plane at theamplifier output, is the ratio of the “reflected” electric field E_(in)heading into the amplifier, to the “outgoing” electric field E_(out)traveling out. Being a ratio of fields, F is a complex number with amagnitude and phase. A useful way to depict changing conditions in asystem is to use a “polar-chart” plot of Γ's behavior (termed a “loadtrajectory”) on the complex plane. Certain regions of the polar chartmay represent unstable regions of operation for the amplifier 124. Theamplifier 124 and phase shift in the feedback loop should be designed sothe load trajectory does not cross an unstable region. The loadtrajectory can be rotated on the polar chart by changing the phase shiftof the feedback loop (by using the phase shifter 130 and/or adjustingthe length of the circuit loop formed by the lamp drive circuit to theextent permitted while maintaining the desired impedance matching. Theload trajectory can be shifted radially by changing the magnitude (e.g.,by using an attenuator).

High frequency simulation software may be used to help select thematerials and shape of the lamp body and electrically conductive coatingto achieve desired resonant frequencies and field intensity distributionin the lamp body. Simulations may be performed using software tools suchas HFSS, available from Ansoft, Inc. of Pittsburgh, Pa., and FEMLAB,available from COMSOL, Inc. of Burlington, Mass. to determine thedesired shape of the lamp body, resonant frequencies and field intensitydistribution. The desired properties may then be fine-tuned empirically.

While a variety of materials, shapes and frequencies may be used, oneexample embodiment has a lamp body 102 designed to operate in afundamental TM resonant mode at a frequency of about 880 MHz (althoughthe resonant frequency changes as lamp operating conditions change asdescribed further below). In this example, the lamp has an alumina lampbody 102 with a relative permittivity of 9.2. The lamp body 102 has acylindrical outer surface as shown in FIG. 1B with a recess 118 formedin the bottom surface. In an alternative embodiment shown in FIG. 1C,the lamp body 102 may have a rectangular outer surface. The outerdiameter D1 of the lamp body 102 in FIG. 1B is about 40.75 mm and thediameter D2 of the recess 118 is about 8 mm. In other examples, thediameter D2 may range from about 4 mm to 10 mm or any range subsumedtherein. The lamp body has a height H1 of about 17 mm. In otherexamples, the height H1 may range from about 10 mm to 30 mm or any rangesubsumed therein. A narrow region 112 forms a shelf over the recess 118.The thickness H2 of the narrow region 112 is about 2 mm and may rangefrom about 1-8 mm in other embodiments or any range subsumed therein. Asshown in FIG. 1A, in this region of the lamp body 102 the electricallyconductive surfaces on the lamp body are only separated by the thinregion 112 of the shelf. This results in higher capacitance in thisregion of the lamp body and higher electric field intensities. Thisshape has been found to support a lower resonant frequency than a solidcylindrical body having the same overall diameter D1 and height H1 or asolid rectangular body having the same overall width and height.

In some embodiments, the relative permittivity of the dielectric lampbody is in the range of about 9-15 or any range subsumed therein, thefrequency of the RF power is less than about 1 GHz and the volume of thelamp body is in the range of about 10 cm³ to 30 cm³ or any rangesubsumed therein. In one example, the relative permittivity is less than10, the frequency is less than 1 GHz and the volume of the lamp body isless than 30 cm³.

In some embodiments, the relative permittivity of the dielectric lampbody is in the range of about 9-15 or any range subsumed therein, thefrequency of the RF power is less than about 2.5 GHz and the volume ofthe lamp body is in the range of about 4 cm³ to 7 cm³ or any rangesubsumed therein. In one example, the relative permittivity is less than10, the frequency is less than 2.5 GHz and the volume of the lamp bodyis less than 7 cm³.

In this example, a hole 110 is formed in the thin region 112. The holehas a diameter of about 5.5 mm and the bulb has an outer diameter ofabout 5 mm. The shelf formed by the thin region 112 extends radiallyfrom the edge of the hole 110 by a distance D3 of about 1.25 mm. D3 mayrange from 0.5 to 5 mm or any range subsumed therein. Alumina powder ispacked between the bulb and the lamp body and forms a layer having athickness D5 of about ¼ mm. The alumina powder has a lower thermalconductivity than the lamp body and avoids cold spots on the bulb.However, the short gap distance provides a higher capacitance betweenthe top and bottom metallic surfaces of the shelf and the impedance ofthe plasma in the bulb. In example embodiments, the gap is as thin aspossible while maintaining desired thermal properties.

In this example, the bulb 104 has an outer length of about 15 mm and aninterior length of about 9 mm. The interior diameter at the center isabout 2.2 mm and the side walls have a thickness of about 1.4 mm. Thebulb protrudes from the front surface of the lamp body by about 4.7 mm.In this example, the bulb has a high pressure fill of Argon at apressure in the range of about 400-750 Torr, Kr₈₅, Mercury and IndiumBromide. At pressures above 400 Torr, a sparker or other ignition aidmay be used for initial ignition. Aging of the bulb may facilitate fillbreakdown, and the fill may ignite without a separate ignition aid afterburn-in of about 72 hours.

In this example, the drive probe 120 is about 15 mm long with a diameterof about 2 mm. The drive probe 120 is about 7 mm from the central axisof the lamp body and a distance D4 of about 3 mm from the electricallyconductive material 108 on the inside surface of recess 118. Therelatively short distance from the drive probe 120 to the bulb 104enhances coupling of power. In example embodiments, the feedback probeis further from the inside surface of the recess. In an exampleembodiment, the distance D6 is about 11 mm. In other examples, D6 mayrange from about 4 mm to 20 mm or any range subsumed therein. In someexamples, the feedback probe may be closer to the outer metal surface ofthe lamp body than the central axis. In some examples, the feedbackprobe may be closer to the outer metal surface of the lamp body than theinner surface of the recess. In one example, a 15 mm hole is drilled forthe feedback probe 122 to allow the length and coupling to be adjusted.The unused portion of the hole may be filled with PTFE (Teflon) oranother material. In this example, the feedback probe 122 has a lengthof about 3 mm and a diameter of about 2 mm. In another embodiment wherethe length of the hole matches the length of the feedback probe 122, thelength of the feedback probe 122 is about 1.5 mm.

In this example, the bulb is positioned adjacent to narrow region 112where the electric field of the radio frequency power in the lamp bodyis at a maximum. In this example, the drive probe 120 and feedback probe122 are not positioned at a maxima or minima of the electric field ofthe radio frequency power in the lamp body. In example embodiments, theposition of the probes may be selected for desired power coupling andimpedance matching.

In this example, the lamp drive circuit 106 includes an attenuator 128,phase shifter 130, amplifier 124, matching network 126 and controlelectronics 132 such as a microprocessor or microcontroller thatcontrols the drive circuit. A sensor 134 detects the intensity of lightemitted by the bulb 104 and provides this information to the controlelectronics 132 to control the drive circuit 132. In an alternativeembodiment, an RF power sensor 136 may be used to detect forward,reflected or net power to be used by the control electronics to controlthe drive circuit.

FIG. 6A is a block diagram of a lamp and drive circuit according to analternate embodiment that uses a switched capacitor to better match theload during startup. FIG. 6B is a flow chart of a method for starting alamp using a switched capacitor. As shown in FIG. 6A, the lamp drivecircuit includes a switched capacitor circuit 602 in parallel betweenthe amplifier 124 and lamp body 102. The controller 132 provides asignal to the switched capacitor circuit 602 that either includes thecapacitance in the impedance matching network between the amplifier 124and the lamp body 102 or remove the capacitance. The controller receivesinputs from a power sensor 636 and/or light sensor 134 to determine whento switch the capacitance. In other embodiments, this may also bedetermined by a timer circuit or other method. Other embodiments mayalso switch other impedance matching circuit elements in and out of thecircuit as the load conditions change. As shown in FIG. 6B the lamp isturned on at 650. The noble gas then ignites and the lamp start phasebegins as indicated at 652. In this example, the capacitance from thecapacitor circuit 602 is included in the circuit as indicated at 654.The capacitance is selected to provide a better impedance match to theload during startup when the resistance in the fill is lower. Thisimproves the power coupling to the plasma during startup and can be usedto decrease startup time. Once the Mercury and metal halide in the fillvaporizes, the load conditions change and the lamp transitions to highbrightness. This transition can be detected based on power from powersensor 636 or light output intensity from photodiode 134 (e.g., 20%-90%of peak intensity or any range subsumed therein). Once the particularlamp operating condition is detected, the capacitor is switched out ofthe circuit as indicated at i 658. This provides for better impedancematching and improved power coupling during run mode.

FIG. 7A is a block diagram of a lamp and drive circuit according to analternate embodiment that uses a variable capacitor to better match theload during startup. FIG. 7B is a flow chart of a method for starting alamp using a variable capacitor. As shown in FIG. 7A, the lamp drivecircuit includes a variable capacitor 702 in parallel between theamplifier 124 and lamp body 102. The controller 132 provides a signal tothe variable capacitor circuit 602 to set the level of capacitance thatis included in the impedance matching network between the amplifier 124and the lamp body 102. The controller receives inputs from a powersensor 636 and/or light sensor 134 to determine when to adjust thecapacitance. In other embodiments, this may also be determined by atimer circuit or other method. Other embodiments may also adjust orswitch other impedance matching circuit elements (which may be inparallel or in series). As shown in FIG. 7B the lamp is turned on at750. The noble gas then ignites and the lamp start phase begins asindicated at 752. In this example, the capacitance from the capacitorcircuit 602 is set to a first value during startup as indicated at 754.The capacitance is selected to provide a better impedance match to theload during startup when the resistance in the fill is lower. Thisimproves the power coupling to the plasma during startup and can be usedto decrease startup time. Once the Mercury and metal halide in the fillvaporizes, the load conditions change and the lamp transitions to highbrightness. This transition can be detected based on power from powersensor 636 or light output intensity from photodiode 134 (e.g., about20%-90% of peak intensity or any range subsumed therein). Once theparticular lamp operating condition is detected, the capacitor isadjusted to a different value for run mode as indicated at 758. Thisprovides for better impedance matching and improved power couplingduring run mode.

The above circuits, dimensions, shape, materials and operatingparameters are examples only and other embodiments may use differentcircuits, dimensions, shape, materials and operating parameters.

1. An electrodeless plasma lamp comprising: a lamp body comprising adielectric material having a relative permittivity greater than 2; abulb proximate the lamp body, the bulb containing a fill that forms aplasma when radio frequency (RF) power is coupled to the fill from thelamp body, the fill including a gas and at least one metal halide; and alamp drive circuit for providing RF power to the lamp body; wherein theRF power is provided to the fill to vaporize the metal halide and emitlight; and wherein the lamp drive circuit is configured to adjust the RFpower provided to the fill after light is emitted by the vaporized metalhalide to maintain a substantially constant brightness as the loadconditions of the plasma change during heat up of the plasma.
 2. Theelectrodeless lamp of claim 1, wherein the lamp drive circuit isconfigured to provide the RF power at a frequency that forms a standingwave within the lamp body.
 3. The electrodeless lamp of claim 1, whereinthe lamp drive circuit is configured to provide the RF power at afrequency that is within the resonant bandwidth of a resonant mode forthe lamp body.
 4. The electrodeless plasma lamp of claim 3, wherein theresonant mode is the fundamental resonant mode for the lamp body.
 5. Theelectrodeless lamp of any of claim 1, 2, 3 or 4, wherein the lamp drivecircuit is configured to adjust the RF power by adjusting the frequencyof the RF power.
 6. The electrodeless plasma lamp of claim 5, whereinthe lamp drive circuit is configured to adjust the frequency of the RFpower frequency by adjusting a phase shifter in the lamp drive circuit.7. The electrodeless plasma lamp of any of claim 1, 2, 3 or 4, whereinthe lamp drive circuit includes an amplifier and a control circuitconfigured to adjust the gain of the amplifier.
 8. The electrodelesslamp of any of claim 1, 2, 3 or 4, wherein the lamp drive circuitincludes a feedback loop that samples power from the lamp body.
 9. Theelectrodeless lamp of claim 5 or claim 6, wherein the lamp drive circuitincludes a feedback loop that samples power from the lamp body.
 10. Theelectrodeless lamp of any of claim 1, 2, 3 or 4, further comprising asensor for detecting a lamp operating condition, wherein the lamp drivecircuit adjusts the RF power in response to a signal from the sensor.11. The electrodeless lamp of claim 10, wherein the sensor is a lightsensor that detects light output intensity from the bulb.
 12. Theelectrodeless lamp of claim 10, wherein the sensor is a power sensor.13. The electrodeless plasma lamp of claim 5, further comprising asensor for detecting a lamp operating condition, wherein the lamp drivecircuit adjusts the frequency in response to a signal from the sensor.14. The electrodeless lamp of claim 13, wherein the sensor is a lightsensor that detects light output intensity from the bulb.
 15. Theelectrodeless lamp of claim 13, wherein the sensor is a power sensor.16. The electrodeless plasma lamp of any of claim 1, 2, 3 or 4, whereinthe lamp drive circuit is configured to adjust the RF power in a seriesof at least 5 adjustments after the output intensity of the bulb reachesa threshold.
 17. The electrodeless lamp of claim 5, wherein thefrequency is ramped down in a series of adjustments after the outputintensity of the bulb reaches a threshold.
 18. The electrodeless lamp ofclaim 16, wherein the threshold is a detected level of brightness thatis within the range of about 10% to 90% of the peak visible brightnessfor the lamp.
 19. The electrodeless lamp of claim 17, wherein thethreshold is a detected level of brightness that is within the range ofabout 10% to 90% of the peak visible brightness for the lamp.
 20. Theelectrodeless lamp of claim 17, wherein the lamp drive circuit isconfigured to adjust the frequency of the RF power by making a series ofadjustments to a phase shifter in the lamp drive circuit.
 21. Theelectrodeless lamp of claim 17, wherein the frequency is ramped in aseries of at least 10 adjustments.
 22. The electrodeless lamp of claim20, wherein the frequency is ramped in a series of at least 10adjustments.
 23. The electrodeless lamp of any of claim 1, 2, 3 or 4,wherein the drive circuit is configured to maintain the brightnesswithin about 3% of a constant value.
 24. The electrodeless lamp of anyof claims 5, wherein the drive circuit is configured to maintain thebrightness within about 3% of a constant value after light is emitted bythe vaporized metal halide.
 25. The electrodeless lamp of any of claims5, wherein the drive circuit is configured to maintain the brightnesswithin about 3% of a constant value after light is emitted by thevaporized metal halide.
 26. An electrodeless plasma lamp comprising: aresonant structure comprising a solid dielectric material and anelectrically conductive material; a bulb proximate the resonantstructure, the bulb containing a fill that forms a plasma when radiofrequency (RF) power is coupled to the fill from the resonant structure,the fill including a gas and at least one metal halide; and a lamp drivecircuit for providing RF power to the resonant structure at a frequencywithin a resonant bandwidth for the resonant structure such that the RFpower is coupled to the fill to vaporize the metal halide and emitlight; wherein the lamp drive circuit is configured to adjust the RFpower provided to the fill after light is emitted by the vaporized metalhalide to maintain a brightness within a range of a constant value asthe load conditions of the plasma change during heat up of the plasma.27. The electrodeless plasma lamp of claim 26, wherein the range isabout 5% of the constant value.
 28. The electrodeless plasma lamp ofclaim 26, wherein the range is about 3% of the constant value.
 29. Theelectrodeless plasma lamp of claim 26, wherein the range is about 1% ofthe constant value.
 30. The electrodeless lamp of claims 26, wherein thelamp drive circuit is configured to adjust the RF power by adjusting thefrequency of the RF power.
 31. The electrodeless plasma lamp of claim30, wherein the lamp drive circuit is configured to adjust the frequencyof the RF power frequency by adjusting a phase shifter in the lamp drivecircuit.
 32. The electrodeless plasma lamp of claim 26, wherein the lampdrive circuit includes an amplifier and a control circuit configured toadjust the gain of the amplifier.
 33. The electrodeless plasma lamp ofany of claim 26, 27, 28, 29, 30, 31 or 32, wherein the lamp drivecircuit is configured to adjust the RF power based on a lamp operatingcondition.
 34. The electrodeless plasma lamp of claim 33, wherein thelamp operating condition is a signal representing the brightness of thelamp.
 35. The electrodeless plasma lamp of claim 33, wherein the lampoperating condition is a signal representing a power level in the lampdrive circuit.
 36. The electrodeless plasma lamp of claim 33, whereinthe solid dielectric material has a volume in the range of about 4 cm³to 30 cm³.
 37. The electrodeless plasma lamp of any of claim 26, 27, 28,29, 30, 31 or 32, wherein the lamp body has a volume in the range ofabout 4 cm³ to 30 cm³.
 38. A method comprising: providing a lamp bodycomprising a dielectric material having a relative permittivity greaterthan 2; positioning a bulb proximate the lamp body, the bulb containinga fill, the fill including a gas and at least one metal halide; couplingpower to the fill through the lamp body to vaporize the metal halide andemit light; and adjusting the RF power after light is emitted by thevaporized metal halide to maintain a brightness within a range of aconstant value as the load conditions of the plasma change during heatup of the plasma.
 39. The method of claim 38, wherein the range is about5% of the constant value.
 40. The method of claim 38, wherein the rangeis about 3% of the constant value.
 41. The method of claim 38, whereinthe range is about 1% of the constant value.
 42. The method of claim 38,39, 40 or 41, wherein adjusting the RF power comprises adjusting thefrequency of the RF power.
 43. The electrodeless plasma lamp of any ofclaim 1, 2, 3, 4, 26, 27, 28, 29, 30, 31 or 32, wherein the bulb has aninterior volume of less than about 100 mm³.
 44. The electrodeless plasmalamp of any of claims 1, 2, 3, 4, 26, 27, 28, 29, 30, 31 or 32, whereinthe net RF power provided by the lamp drive circuit is at least 100watts after the vaporization of the metal halide.
 45. The electrodelessplasma lamp of claim 43, wherein the net RF power provided by the lampdrive circuit is at least 100 watts after the vaporization of the metalhalide.
 46. The electrodeless plasma lamp of claim 43, wherein the netRF power provided by the lamp drive circuit is less than 100 watts priorto the vaporization of the metal halide.
 47. The electrodeless plasmalamp of claim 44, wherein the net RF power provided by the lamp drivecircuit is less than 100 watts prior to the vaporization of the metalhalide.
 48. The electrodeless plasma lamp of claim 45, wherein the netRF power provided by the lamp drive circuit is less than 100 watts priorto the vaporization of the metal halide.
 49. An electrodeless plasmalamp comprising: a resonant structure comprising a solid dielectricmaterial and an electrically conductive material; a bulb proximate theresonant structure, the bulb containing a fill that forms a plasma whenradio frequency (RF) power is coupled to the fill from the resonantstructure, the fill including a gas and at least one metal halide; and alamp drive circuit for providing RF power to the resonant structure at afrequency within a resonant bandwidth for the resonant structure suchthat the RF power is coupled to the fill to vaporize the metal halideand emit light; the lamp drive circuit including an amplifier and animpedance control circuit configured to adjust an impedance between theamplifier and the resonant structure.
 50. The electrodeless plasma lampof claim 49, wherein the impedance includes a variable capacitor. 51.The electrodeless plasma lamp of claim 49, wherein the impedance controlcircuit is configured to adjust the impedance by adjusting a capacitancein the lamp drive circuit.
 52. The electrodeless plasma lamp of claim49, wherein the impedance control circuit is configured to adjust theimpedance by switching an impedance element in the lamp drive circuit.53. The electrodeless plasma lamp of any of claim 49, 50, 51 or 52,wherein the impedance control circuit is configured to adjust theimpedance based on a lamp operating condition.
 54. The electrodelessplasma lamp of any of claim 49, 50, 51 or 52, wherein the impedancecontrol circuit is configured to adjust the impedance from a firstimpedance prior to vaporization of the metal halide to a secondimpedance after vaporization of the metal halide.
 55. The electrodelessplasma lamp of any of claim 49, 50, 51 or 52, wherein the impedancecontrol circuit comprises a timer circuit configured to determine thetime at which to adjust the impedance.
 56. The electrodeless plasma lampof any of claim 49, 50, 51 or 52, wherein the bulb has an interiorvolume of less than about 100 mm³.
 57. The electrodeless plasma lamp ofany of claim 49, 50, 51 or 52, wherein the net RF power provided by thelamp drive circuit is at least 100 watts after the vaporization of themetal halide.
 58. The electrodeless plasma lamp of claim 56, wherein thenet RF power provided by the lamp drive circuit is at least 100 wattsafter the vaporization of the metal halide.
 59. The electrodeless plasmalamp of any of claim 49, 50, 51 or 52, wherein the solid dielectricmaterial has a volume in the range of about 4 cm³ to 30 cm³.
 60. Theelectrodeless plasma lamp of claim 56, wherein the solid dielectricmaterial has a volume in the range of about 4 cm³ to 30 cm³.
 61. Theelectrodeless plasma lamp of claim 58, wherein the solid dielectricmaterial has a volume in the range of about 4 cm³ to 30 cm³.
 62. Anelectrodeless plasma lamp comprising: a bulb containing a fill thatforms a plasma; a power amplifier for providing radio frequency power tothe plasma at a frequency in the range of about 50 MHz to 10 GHz, thepower amplifier capable of operating in at least two classes ofoperation; and control electronics configured to change the class ofoperation of the power amplifier.
 63. The plasma lamp of claim 62,further comprising a light sensor for detecting light output intensityfrom the bulb, wherein the control electronics is configured to changethe class of operation of the power amplifier in response to a signalfrom the light sensor.
 64. The plasma lamp of claim 62, furthercomprising a power sensor for detecting power provided by the poweramplifier, Wherein the control electronics is configured to change theclass of operation of the power amplifier in response to a signal fromthe power sensor.
 65. The plasma lamp of any of claim 62, 63 or 64,wherein the control electronics is configured to change the class of thepower amplifier by changing a gate bias of the power amplifier.
 66. Theplasma lamp of any of claim 62, 63 or 64, further comprising a lamp bodyand a first radio frequency feed coupled to the power amplifier toprovide radio frequency power to the lamp body, wherein the bulb isadjacent to the lamp body and the plasma receives the radio frequencypower from the lamp body.
 67. The plasma lamp of claim 66 wherein: thepower amplifier is configured to provide RF power at a frequency thatforms a standing wave within the lamp body.
 68. The plasma lamp of claim66 wherein: the lamp body comprising a dielectric material having arelative permittivity greater than 2; and the power amplifier isconfigured to provide RF power at a frequency that is within theresonant bandwidth of a resonant mode for the lamp body.
 69. The plasmalamp of any of claim 62, 63 or 64 wherein: the power amplifier isconfigured to operate as a class A/B amplifier during at least a firstmode of operation and a class C amplifier during at least a second modeof operation.
 70. The plasma lamp of claim 69, wherein the first mode ofoperation is a startup mode during which the plasma warms up.
 71. Theplasma lamp of claim 69, wherein the second mode of operation is steadystate operation above a threshold level of brightness.
 72. The plasmalamp of claim 70, wherein the second mode of operation is steady stateoperation above a threshold level of brightness.
 73. The plasma lamp ofclaim 69, wherein the first mode of operation is a mode during which theplasma lamp operates below a threshold level of brightness.
 74. Theplasma lamp of claim 73 wherein the threshold is in the range of about50% to 80% of peak brightness.
 75. An electrodeless plasma lampcomprising: a bulb containing a fill that forms a plasma; a poweramplifier for providing radio frequency power to the plasma at afrequency in the range of about 50 MHz to 10 GHz; and controlelectronics configured to change the gate bias voltage of the poweramplifier.
 76. The plasma lamp of claim 75, further comprising a lightsensor for detecting light output intensity from the bulb, wherein thecontrol electronics is configured to change the gate bias voltage of thepower amplifier in response to a signal from the light sensor.
 77. Theplasma lamp of claim 75, further comprising a power sensor for detectingpower provided by the power amplifier, wherein the control electronicsis configured to change the gate bias voltage of the power amplifier inresponse to a signal from the power sensor.
 78. The plasma lamp of anyof claim 75, 76, or 77, further comprising: a resonant structurecomprising a solid dielectric material and an electrically conductivematerial, the resonant structure proximate the bulb; wherein the poweramplifier provides radio frequency power to the resonant structure at afrequency within a resonant bandwidth for the resonant structure. 79.The electrodeless plasma lamp of claim 78; wherein the bulb has aninterior volume of less than about 100 mm³.
 80. The electrodeless plasmalamp of claim 78, wherein the net RF power provided by the lamp drivecircuit is at least 100 watts after the vaporization of the metalhalide.
 81. The electrodeless plasma lamp of claim 80; wherein the netRF power provided by the lamp drive circuit is at least 100 watts afterthe vaporization of the metal halide.
 82. The electrodeless plasma lampof claim 78, wherein the solid dielectric material has a volume in therange of about 4 cm³ to 30 cm³.
 83. The electrodeless plasma lamp ofclaim 79, wherein the solid dielectric material has a volume in therange of about 4 cm³ to 30 cm³.
 84. The electrodeless plasma lamp ofclaim 80, wherein the solid dielectric material has a volume in therange of about 4 cm³ to 30 cm³.
 85. A method comprising: providing abulb containing a fill that forms a plasma; coupling power from anamplifier to the plasma at a frequency in the range of about 50 MHz to10 GHz; and adjusting the gate bias voltage of the power amplifier. 86.The method of claim 85, wherein adjusting the gate bias voltage is basedon a detected lamp operating condition.
 87. An electrodeless plasma lampcomprising: a lamp body comprising a dielectric material having arelative permittivity greater than 2; a bulb adjacent to the lamp body,the bulb containing a fill that forms a plasma when RF power is coupledto the fill from the lamp body; an RF feed coupled to the lamp body; anda radio frequency (RF) power source for coupling power into the lampbody through the RF feed, the RF power source configured to provide RFpower at a frequency that forms a standing wave within the lamp body;wherein the shortest distance between an end of the bulb and an end ofthe RF feed traverses at least one electrically conductive material ofthe lamp body.
 88. The electrodeless plasma lamp of claim 87, whereinthe electrically conductive material is spaced apart from the bulb andthe drive probe.
 89. The electrodeless plasma lamp of claim 87, whereinthe distance from the end of the bulb to the end of the RF feed is lessthan about 10 mm.
 90. The electrodeless plasma lamp of claim 87, whereinthe distance from the end of the bulb to the end of the RF feed isgreater than a distance from a side of the bulb to the end of the probe.91. The electrodeless plasma lamp of claim 87 wherein a distance fromthe end of the bulb to the electrically conductive material is less thanabout 5 mm.
 92. The electrodeless plasma lamp of any of claim 87, 88,89, 90 or 91 wherein a distance from the end of the probe to theelectrically conductive material is less than about 10 mm.
 93. Theelectrodeless plasma lamp of any of claim 87, 88, 89, 90 or 91 wherein adistance from the end of the probe to the electrically conductivematerial is less than about 5 mm.
 94. The electrodeless plasma lamp ofany of claim 87, 88, 89, 90 or 91 wherein a distance from the end of theprobe to a central axis of the lamp body is less than about 15 mm. 95.The electrodeless plasma lamp of any of claim 87, 88, 89, 90 or 91wherein a distance from the end of the probe to a central axis of thelamp body is less than about 10 mm.
 96. The electrodeless plasma lamp ofclaim 95 wherein the bulb is positioned such that at least a portion ofthe bulb intersects the central axis.
 97. The electrodeless plasma lampof claim 96 wherein the bulb is positioned such that at least a portionof the bulb intersects the central axis.
 98. The electrodeless plasmalamp of any claim 87, 88, 89, 90 or 91 wherein the interior bulb volumeis less than about 100 mm³.
 99. The electrodeless plasma lamp of any ofclaim 87, 88, 89, 90 or 91 wherein the RF feed is a probe having adiameter greater than about 1.5 mm.
 100. The electrodeless plasma lampof claim 87, 88, 89, 90 or 91 wherein the drive probe has a lengthgreater than about 10 mm.
 101. An electrodeless plasma lamp comprising:a resonant structure comprising a solid dielectric material and anelectrically conductive material; a bulb proximate the resonantstructure, the bulb containing a fill that forms a plasma when RF poweris coupled to the fill from the resonant structure; and a probeconfigured to couple the RF power into the resonant structure at afrequency within the resonant bandwidth for the resonant structure,wherein an end of the probe is spaced apart from the electricallyconductive material by the solid dielectric material; wherein thedistance between the end of the probe and the electrically conductivematerial is in the range of about 1 mm to 10 mm.
 102. The electrodelessplasma lamp of claim 101, wherein the distance between the end of theprobe and the electrically conductive material is less than about 5 mm.103. The electrodeless plasma lamp of claim 101, wherein the distancebetween the end of the probe and the electrically conductive material isless than about 3 mm.
 104. The electrodeless plasma lamp of claim 101,wherein a distance from the end of the probe to a central axis of theresonant structure is less than about 15 mm.
 105. The electrodelessplasma lamp of claim 101, wherein a distance from the end of the probeto a central axis of the resonant structure is less than about 10 mm.106. The electrodeless plasma lamp of claim 101, wherein a distance fromthe end of the probe to a central axis of the resonant structure isgreater than about 5 mm.
 107. The electrodeless plasma lamp of claim105, wherein a distance from the end of the probe to a central axis ofthe resonant structure is greater than about 3 mm.
 108. Theelectrodeless plasma lamp of claim 101, wherein a distance from the endof the probe to the bulb is less than about 10 mm.
 109. Theelectrodeless plasma lamp of any of claim 101, 102, 103, 104, 105, 106,107 or 108, wherein the bulb has an interior volume of less than about100 mm³.
 110. The electrodeless plasma lamp of claim 109, wherein thenet RF power provided by the lamp drive circuit is at least 100 wattsafter the vaporization of the metal halide.
 111. The electrodelessplasma lamp of any of claim 101, 102, 103, 104, 105, 106, 107 or 108,wherein the net RF power provided by the lamp drive circuit is at least100 watts after the vaporization of the metal halide.
 112. Theelectrodeless plasma lamp of any of claim 101, 102, 103, 104, 105, 106,107 or 108, wherein the solid dielectric material has a volume in therange of about 4 cm³ to 30 cm³.
 113. The electrodeless plasma lamp ofclaim 109, wherein the solid dielectric material has a volume in therange of about 4 cm³ to 30 cm³.
 114. The electrodeless plasma lamp ofclaim 110, wherein the solid dielectric material has a volume in therange of about 4 cm³ to 30 cm³.
 115. The electrodeless plasma lamp ofclaim 111, wherein the solid dielectric material has a volume in therange of about 4 cm³ to 30 cm³.
 116. The electrodeless plasma lamp ofany of claim 101, 102, 103, 104, 105, 106, 107 or 108, wherein the soliddielectric material has a volume in the range of about 4 cm³ to 7 cm³.117. The electrodeless plasma lamp of claim 109, wherein the soliddielectric material has a volume in the range of about 4 cm³ to 7 cm³.118. The electrodeless plasma lamp of claim 110, wherein the soliddielectric material has a volume in the range of about 4 cm³ to 7 cm³.119. The electrodeless plasma lamp of claim 111, wherein the soliddielectric material has a volume in the range of about 4 cm³ to 7 cm³.120. The electrodeless plasma lamp of claim 109, wherein the frequencyis less than about 1 GHz.
 121. The electrodeless plasma lamp of claim110, wherein the frequency is less than about 1 GHz.
 122. Theelectrodeless plasma lamp of claim 111, wherein the frequency is lessthan about 1 GHz.
 123. The electrodeless plasma lamp of claim 112,wherein the frequency is less than about 1 GHz.
 124. The electrodelessplasma lamp of claim 113, wherein the frequency is less than about 1GHz.
 125. The electrodeless plasma lamp of claim 114, wherein thefrequency is less than about 1 GHz.
 126. The electrodeless plasma lampof claim 115, wherein the frequency is less than about 1 GHz. GHz. 127.The electrodeless plasma lamp of claim 116, wherein the frequency isless than about 2.5 GHz.
 128. The electrodeless plasma lamp of claim117, wherein the frequency is less than about 2.5 GHz.
 129. Theelectrodeless plasma lamp of claim 118, wherein the frequency is lessthan about 2.5 GHz.
 130. The electrodeless plasma lamp of claim 119,wherein the frequency is less than about 2.5 GHz.